More Than Meets the Eye: How the CCD Transformed Science

The 2009 Nobel Prize for Physics went, in part, to the inventors of the charge-coupled device George Smith and Willard Boyle this week. Their innovation, sketched out in 1969, is now the imager in millions of digital cameras and telescopes.

The very first prototype, pieced together months after Smith and Boyle laid out its working principles, is pictured above.

A charge-coupled device, in most applications, translates light into an electronic signal. Photons of light striking an array of capacitors create an electrical charge proportional to their intensity, which the charge-coupler transforms into voltage. That signal can be digitized and transformed by the dull magic of high-performance computing into Hubble’s images.

Millions of CCDs are made each year for mass market cameras, but they also proved a transformational technology in science by providing a much more sensitive light sensor than previously existed. After being overlooked for decades, the Nobel win was a mild surprise but well deserved.

“There wasn’t anything that could compete in scientific imaging,” said Tony Tyson, an astronomer at the University of California, Davis, who built the first CCD camera for scientific applications in the late 1970s. “You’re interested in getting very high signal-to-noise ratios. There’s nothing that really competes with CCDs.”

For the really dim things astronomers look at, the number of photons of light coming from a source is so small that each one counts. Out of every 100 photons, a CCD can record more than 90 of them. Photographic plates can barely reach 10 percent. And your eyes? Their quantum efficiency is in the 1 to 4 percent range.

According to lore, Smith and Boyle sketched out the design for the ubiquitous imaging device in an hour, over lunch at Bell Labs in October 1969. Working under the intense pressure applied by their taskmaster of a boss, Jack Morton, the pair had the device fabricated within a couple of months. George Smith took a photo of it, which you can see at the top of the page.

The road, though, from the creation of the prototype to the development of an actual technology that could be used by scientists and photographers was long and hard. Though CCDs would come to dominate astronomy, the device, as invented, was nowhere near high enough resolution to be worthwhile. With its poor signal-to-noise ratio, it was not immediately clear that the CCD was destined for greatness.

“I joined the company in 1969, the very year that Dick Boyle and George Smith invented this thing,” Tyson said. “I actually, frankly viewed it as a toy. It was so small and awfully noisy.”

Historians Robert W. Smith and Joseph N. Tararewicz note that “astronomers could not simply procure a CCD ‘off the shelf’ soon after the device’s invention at Bell Labs.” In fact, a number of other imaging systems were suggested for what became the Hubble Space Telescope including a panoply of image tubes.

Some astronomers, though, saw the potential for CCDs down the road. They were in Smith and Tararewicz’s terms, “counting on invention.”

In the face of budget cuts in 1974 that threatened the installation of the still speculative, expensive CCD technology on the Large Space Telescope (Hubble), an astronomer delivered an impassioned plea for the technology.

“To decide now, eight years before the LST can possibly fly, on what is already an out-dated detector, less than state-of-the-art, will be regarded in the future, I think as a poor choice of the options which are conceivable in other directions for cutting the cost of the LST,” Margaret Burbidge, a prominent astrophysicist, wrote. “It is like deciding to treat a sick patient by cutting out his heart on the grounds he would be saved the energy used by the heart muscles in pumping the blood around the body.”

Hard work by hundreds of scientists and engineers pushed CCDs closer to reality over the next few years. Companies like Fairchild, Kodak and Tektronix, rather than Bell Labs, developed the technology into usable form. Military, scientific and consumer applications were all benefiting from the money being thrown at the CCD problems from different directions, but it was still tough.

“It was a very painful development,” Tyson said. “There were all these problems making really large cameras and getting uniform CCDs out of companies that were already pushing the envelope.”

Still, scientists like Tyson persevered. After nearly a decade, he put his latest camera on the 40-inch telescope at Mt. Palomar Observatory and was able to measure the distribution of the faint blue galaxies. That work became an important piece of evidence that dark energy — the mysterious force propelling the acceleration of the universe outward — actually exists.

Now, nearly every major astronomical observatory uses CCDs. They also remain the gold-standard for medical imaging, or really any type of science that needs to capture photons. Though CMOS imaging technology is making inroads in consumer technology, there’s “still nothing like a huge CCD,” Tyson said, for high-end science.

Tyson’s latest project is the Large Synoptic Sky Survey, which will incorporate a 3,200-megapixel camera. Plotted against time, CCD performance, measured in pixels, has grown at close to the same dizzying logarithmic rate that computing power has (see below).

Clearly, that hour of lunch at Bell Labs opened up a technological development path that was as broad and deep as nearly any in the 20th century. And after decades of being overlooked for the biggest prize in science, the inventors of the CCD are finally getting their due.

“Back, say, 30 years ago when I was at Bell Labs, we thought that CCDs could very well be a Nobel Prize,” said Cherry Murray, dean of engineering and physical science at Harvard University and a one-time colleague of Smith and Boyle at Bell Labs. “It had been overlooked for so long … It’s nice to see.”